Q.Explain the following phases of Oogenesis :
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Oogenesis: The Making of an Egg Cell
Think of oogenesis as the biological story of how a female body creates the single most important cell she will ever produce — the egg, or ovum. If you've ever seen a seed that contains everything needed to grow a new plant, you have the right mental picture. The egg cell is that seed for human life. But unlike a seed that sits waiting, the egg cell goes through a long, carefully timed process before it is ready.
The Everyday Intuition
Imagine a factory that makes one very special product. This factory starts its work even before the product is ordered. It prepares the raw materials, stores them for years, and then, when the time is right, finishes the product in a matter of days. That is oogenesis. A female is born with all the "raw materials" she will ever have — millions of tiny, immature egg precursors. Most of these will never be used. Only a few hundred will ever mature into eggs that can be fertilized.
The Precise Meaning
Oogenesis is the process by which the female gamete, or egg cell, is formed in the ovaries. It begins before a girl is even born, pauses for years, and then resumes each month from puberty until menopause. The entire process transforms a primitive cell called an oogonium into a mature ovum (egg) that can be fertilized by a sperm.
The word "oogenesis" comes from Greek: oion meaning "egg" and genesis meaning "origin" or "creation." So it literally means "the origin of the egg."
Why It Matters
You might wonder why a commerce or humanities student needs to know this. Here is why: oogenesis is the biological foundation of female fertility, reproduction, and even the timing of a woman's life. It explains:
- Why a woman is born with all her eggs and never makes new ones.
- Why fertility declines with age — the eggs age along with the woman.
- Why only one egg is released each month, not hundreds like sperm.
- Why the egg is so much larger than a sperm — it carries the cytoplasm, nutrients, and mitochondria that the embryo will need for its first few days.
Key Stages in Simple Terms
The NCERT textbook describes oogenesis in three main phases, but you can think of them as three acts of a play:
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Multiplication phase — Before birth, the oogonia (the stem cells) multiply rapidly. This happens only in the fetal ovary. By the time a female is born, all the oogonia have transformed into primary oocytes, and no new ones are ever made.
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Growth phase — Each primary oocyte grows in size and accumulates nutrients. But then it stops. It enters a resting state called prophase I and stays there for years — until the female reaches puberty. Some primary oocytes wait for 12, 20, or even 40 years before they resume development.
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Maturation phase — After puberty, each month a few primary oocytes start maturing. But only one usually completes the process. This phase involves two rounds of cell division (meiosis I and meiosis II) that reduce the chromosome number by half. The result is one large, functional egg and three tiny, non-functional cells called polar bodies that eventually degenerate. …
Oogenesis proceeds through three distinct phases, each corresponding to a different stage of the germ cell's development, from mitotic multiplication through to a mature ovum. …
Oogenesis is the formation of the mature female gamete (ovum) from oogonia, occurring in three phases — multiplication, growth, and maturation.
Oogenesis is the process of formation of a mature female gamete (ovum) in the ovary, occurring in three phases:
- Multiplication phase: The primordial germ cells in the foetal ovary undergo repeated mitotic divisions, increasing in number to form oogonia. This phase occurs entirely during foetal (embryonic) development — no new oogonia are formed after birth.
- Growth phase: Each oogonium grows in size by accumulating nutrients (yolk) and cytoplasm, becoming a primary oocyte. The primary oocyte then enters the first meiotic division (Meiosis I), but this division gets arrested at the diplotene stage of prophase I, and remains arrested until the female reaches puberty. Each primary oocyte gets surrounded by a layer of granulosa cells to form the primary follicle, and many of these primary follicles get surrounded by additional layers to form secondary and tertiary follicles.
- Maturation phase: …
Showing the 12 most recent of 19 on this concept.
- CBSE 2026Set A1 markMCQQ.Which of the following cells is haploid?(a) Oogonia(b) Primary oocyte(c) Secondary oocyte(d) All of these
›Reveal solutionSolution
The secondary oocyte is haploid because it forms after meiosis I; oogonia and primary oocytes are diploid.
Oogenesis begins with diploid oogonia, which grow into diploid primary oocytes (2n). The primary oocyte then completes the first meiotic division (meiosis I), producing a haploid secondary oocyte (n) and a first polar body. Because chromosome number is halved in meiosi …
- CBSE 2026Set ZOOLOGY1 markMCQQ.What is the discharge of matured egg from the Graafian follicle called as?(a) Oogenesis(b) Fertilization(c) Ovulation(d) Abortion
›Reveal solutionSolution
Ovulation is the process by which a mature egg is released from the ruptured Graafian follicle.
During the menstrual cycle, a primary follicle in the ovary matures into a fully developed Graafian follicle under the influence of FSH. A surge in Luteinising Hormone (LH) around the 14th day of the cycle causes the Graafian follicle to rupture and release the secondary oocyte (egg) into the fallopian tube - this event is called ovulati …
- CBSE 2026Set ANNUAL1 markMCQQ.The remaining parts of the Graafian follicle after ovulation change into –(a) Corpus luteum(b) Ovum(c) Oocyte(d) Secondary Oocyte
›Reveal solutionSolution
The ruptured Graafian follicle left behind after the ovum is released transforms into the corpus luteum, the progesterone-secreting body of the ovarian cycle.
During the ovarian cycle the mature (Graafian) follicle ruptures at ovulation and releases the secondary oocyte. The follicle is not lost — the remaining granulosa cells and theca interna cells enlarge, accumulate a yellow lipid pigment (lutein) and are converted into the corpus luteum ("yellow body").
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- CBSE 2026Set ANNUAL1 markQ.The process of release of ovum from the mature follicle is called _________.
›Reveal solutionSolution
The blank is ovulation — the release of the ovum from the mature (Graafian) follicle around mid-cycle, triggered by the LH surge.
In the CBSE/NCERT Human Reproduction chapter, the ovarian follicle matures into a Graafian follicle. A sharp surge of Luteinising Hormone (LH) at about day 14 of the menstrual cycle ruptures the fol …
- CBSE 2025Set A1 markMCQQ.The process of ovulation induced by the hormone is -(a) LH(b) TSH(c) ACTH(d) STH
›Reveal solutionSolution
Ovulation is triggered by a sudden surge in luteinising hormone (LH) at mid-cycle.
During the menstrual cycle, rising estrogen from the growing Graafian follicle causes a rapid, large rise in luteinising hormone (LH) secreted by the anterior pituitary — the 'LH surge' — around the 14th day of a 28-day cycle. This LH surge induces rupture of the mature Graafian follicle and release of the ovum into the fallopian tube, a process called ovulation. LH also stimulates the remaining follicular tissue to transform into th …
- CBSE 2025Set A1 markQ.Write True / False: Carpus luteum is found in Testis.
›Reveal solutionSolution
The statement is False: the corpus luteum is an ovarian structure, formed in females after ovulation.
After ovulation, the remnants of the ruptured Graafian follicle in the ovary transform into a yellowish glandular structure called the corpus luteum, which secretes progesterone to maintain the uterine lining (endometrium) for possible implantation and pregnancy. The testis is the male gonad and has no corpus luteum; instead, it contains seminiferous tubules (where spermatogenesis occur …
- CBSE 2024Set E1 markMCQQ.After ovulation the ovum is surrounded by a group of cells called(a) Corona radiata(b) Zona pellucida(c) Granulosa cells(d) Theca layer
›Reveal solutionSolution
The ovum released at ovulation is surrounded by follicular cells that form the corona radiata.
At ovulation the secondary oocyte is released along with its surrounding coverings. The innermost non-cellular glycoprotein layer immediately around the oocyte is the zona pellucida. Outside the zona pellucida lies a group/layer of follicular (granulosa) cells radially arranged, which is called the corona radiata. Thus the ovum is 'surrounded by a group of cells' — the corona r …
- CBSE 2024Set E1 markMCQQ.Which of the following cells is haploid?(a) Oogonia(b) Primary oocyte(c) Secondary oocyte(d) Zygote
›Reveal solutionSolution
Among the listed cells only the secondary oocyte is haploid.
During oogenesis, oogonia (2n) multiply by mitosis and enlarge into primary oocytes (2n), which are diploid. The primary oocyte then completes the first meiotic division to give a haploid (n) secondary oocyte and a first polar body. Fertilisation of the secondary oocyte restores diploid …
- CBSE 2024Set D1 markQ.Fill in the blank: The process of release of ovum from a mature follicle is called ______.
›Reveal solutionSolution
The release of the mature ovum from the ruptured Graafian follicle of the ovary, roughly midway through the menstrual cycle, is termed ovulation.
The menstrual cycle has three main phases: the follicular phase, ovulation, and the luteal phase. During the follicular phase, a primary follicle in the ovary grows into a fully mature Graafian follicle under the influence of FSH and LH.
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- CBSE 2024Set D1 markQ.Match the following and write the correct pair. Column 'A':(i) Structural genes(ii) T-Lymphocytes(iii) Competition(iv) PBR322(v) Corona radiata. Column 'B':(a) bone marrow(b) vectors(c) ovum(d) detrimental interaction(e) z, y and a(f) RBCs. Find the correct match for item(v) 'Corona radiata' from Column 'B'.
›Reveal solutionSolution
'Corona radiata' pairs with option (c) 'ovum' — it is the layer of cells that immediately surrounds the released ovum.
When a mature ovum is released from the Graafian follicle during ovulation, it does not exit alone. It remains surrounded by two protective layers: an inner, thick, transparent, non-cellular glycoprotein layer called the zona pellucida, and an outer layer of follicular (granulosa) cells called the corona radiata.
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- CBSE 2023Set ANNUAL1 markMCQQ.At which stage does oogenesis start in human female?(a) During embryonic development(b) At puberty(c) During menarche(d) During menopause
›Reveal solutionSolution
Oogenesis is initiated in the foetal ovary itself; the oocytes then arrest in prophase I of meiosis until they resume development after puberty, one at a time, in each menstrual cycle.
In the human female foetus, millions of oogonia (about 6–7 million) are produced by mitotic divisions inside the developing ovary. Most degenerate, but the surviving ones enter meiosis I and get arrested at the prophase-I stage — these are called primary oocytes, and every female is born with a fixed stock of them (about 1–2 million at birth, further reduced to ~60,000–80,000 by puberty). Meiosis I is completed only just before each ovulation, after puberty, converting a primary oocyte in …
- CBSE 2023Set ANNUAL1 markMCQQ.The number of ovum produced from one primary oocyte is(a) 1(b) 2(c) 3(d) 4
›Reveal solutionSolution
Unlike spermatogenesis, oogenesis divides the cytoplasm unequally at each meiotic division, so nearly all the cytoplasm — and hence functionality — ends up in just one cell: the ovum.
A primary oocyte undergoes meiosis I to form a secondary oocyte and a small first polar body (with very little cytoplasm). The secondary oocyte then undergoes meiosis II (completed only upon fertilisation) to form the mature ovum and a second polar body. Although meiosis technically produces up to four haploid cells (as in spermatogenesis, which gives four functional sperm), in oogenesis the polar bodies are non-fu …
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